1. Field of The Invention
The present invention relates generally to molded case circuit breakers. The present invention relates particularly to protection of the drive pins, blade carrier-to-drive pin interfaces, and surrounding regions of the interrupter modules from contaminants during circuit interruption.
2. Discussion of Related Art
A known type of circuit breaker commonly called a molded case circuit breaker (MCCB) includes a case containing multiple circuit interrupters of a modular type for multiple poles, being commonly for different phases of a three phase electrical system. Typically, the breaker has 3 or 4 poles coupled together with common drive pins.
The circuit interrupter modules are connected by the drive pins to a common drive mechanism for allowing the circuit breaker contacts to separate. The movable contacts causing the separation of current carrying contacts within each module are carried on a blade contained on a rotating blade carrier contained in each module. The common drive pins extend through each of the blade carriers of the separate modules. A common drive mechanism imparts a rotation on the drive pins which in turn rotates the blade carriers to open the circuit of all the poles.
In the known art there are bushings in the form of discs with low coefficient of friction placed between the blade carrier and the module sides. In some systems the bushings are made to tightly fit as a cap to the blade carriers, as in for example U.S. Pat. No. 6,965,292. In other systems, the bushings are not connected to the blade carriers but are fitted in bearing races of the module sides which carry the blade carriers.
Circuit interruption results in expanding arc gases which may force the halves of the interrupter module apart. Contaminates produced by arc interruption and carried by the gases result in the degradation of the dielectric levels inside and between the modules. Under some conditions contaminants of an electrically conductive nature may infiltrate the space between, and regions surrounding, the drive pin and the blade carrier and accumulate there, thus reducing dielectric strength between phases or poles of the circuit breaker. The drive pins becoming contaminated with conductive material may produce an electrical path thus enabling a cross-phase short circuit.